A little bit if an aside, but I attended a local "block party" where my in-law's neighbors all gathered to socialize -- and frankly to show off their various toys (classic wooden boats, vintage cars, etc...) I think my Father-in-law was happy to ride up in the ol' Pagoda... but I digress.
One owner of a very cool restored Porsche 356 had what appeared to be original yellow on black California plates. I commented on them and he whispered ("I painted them!") My originals are long gone but I do have some retired Yellow on Blue ones. Probably illegal to tamper with them but if they are registered -- unlikely anyone would figure it out.